I am having some frustrating problems with my P8P67 Pro motherboard.
This is a new build:
Intel Sandy Bridge 2600k
Asus P8P67 Pro
Mushkin Enhanced Blackline 2x4GB (8GB)
AMD Radeon 6950
Crucial C300 RealSSD 256GB Sata III
Kingston SSDNow 64GB
I had the Crucial SSD with a sata III cable into the first Intel Sata III port. And the Kingston SSD in one of the Sata II ports.
On first boot i was asked to press F1 to enter the bios. My first alarm was that the Crucial SSD was not an option for boot priority, however the kingston and an external usb dvd drive were. I looked in advanced mode and the crucial SSD appeared as an option for boot OVERRIDE but not selecting boot priority.
To make things easy I did no overclocking at all and the ram is even running at 1333, which I haven't tried to increase until I figure this issue out.
When I booted up with the Windows 7 64bit DVD I chose to creat a partition on the Crucial SSD where I was warned that my BIOS did not recognize it as a bootable drive so windows created an extra bootable partition on the drive.
I was able to complete that first stage of the windows install without problem.
After windows attempted to reboot my system began an endless loop of boot up and reboot. It would for a nanosecond flash on the screen Marvell. No boot Device. Or something of that nature, it was difficult to see since it went so fast. I couldn't enter bios either inspite of rapid pressing of the DEL key.
Disgruntled I turned off the power, unplugged the AC and removed the Kingston SSD. This time when I powered on I was able to get into the bios and suprize the Crucial SSD now appears as an option in the boot priority. I completed windows install 100% with everything updated and even played some games with great performance. I did AS SSD Benchmark and confirmed I was getting Sata III Speeds.
With everything working I tried to reconnect the Kingston drive and boot up again. The previous problem returned. It would endlessly cycle with booting up and rebooting. During this the BootLED was lit Red.
I removed the kingston drive again and observed the motherboard during boot. Even without it a red light would appear at the VGA CPU RAM and finally Boot. Then it would appear to reboot and it booted fine with no LED's (crucial only).
Can anyone supply any suggestions as to why this is happening? I find it hard to believe the board is intented to only support a single sata device when there are in fact 8 ports.
I also find it stange that the setting for IDE/RAID/AHCI applies to every sata port and the only option for individual ports is the enable hotswap or not.

I was having issues with the marvell chipset. Use only the intel if you can. Then disable teh marvell. It had issues with just having it enabled. Also, make sure you see those drives and I have my intel sata set to raid. (I do have a raid set up as well). The ssd (I have the exact same one as you sataIII and I have a sataII OCZ vertex2 so my setup sounds just like yours. The top two are the 6G ports. Put the ssd's there. Then if the marvell is disabled, you should be tight. I know I am. If you STILL have issues, I would contact support. It could be either an incompatibility, or something maybe messed up.

I am using all 6 ports on my intel controller with it in raid mode.

3 1TB drives in a stripe, 2 ssd, and a blue ray burner. All happy as clams. FAST as hell.

Thanks for the suggestions.
I am in fact using the Intel SATA III Ports as you said. From what I've observed disabling the Marvell chip is very logical. I wanted to try that at the beginning but I never could find where to actually disable it in the BIOS. In advanced mode all I could see to disable was Hotswap functionality. Maybe I have an old bios firmware?

Ok, well I disabled the Marvell controllers in the bios as recommended. I tried to reconnect the Kingston SSD and the problem from before continues.
The only change is that I dont see the Marvell warning "No Bootable Drive" I was getting before.
I was forced to remove the kingston drive again.
You would think maybe the kingston drive is bad but I was using it as an OS drive a few days ago and It recognized it fine when only the kingston drive was connected, not the C300.

Ok I flashed to 1053. I still can't get past the endless boot failure loop with the kingston drive connected. I tried as you said with just the kingston. The same thing happens that way too. The really bizarre part is that originally the system wanted to boot off of my kingston drive. I know the drive is OK because I used it as an OS drive a few days ago. Its currently reformatted from within Win 7 Setup.
If the drive was the problem I dont see how that could be stopping my system from posting and getting into bios.
I have the kingston in one of the Sata II ports. In a few days I'm going to try to install a sata DVD burner. I'll see if maybe these ports are just bad.

Ok I flashed to 1053. I still can't get past the endless boot failure loop with the kingston drive connected. I tried as you said with just the kingston. The same thing happens that way too. The really bizarre part is that originally the system wanted to boot off of my kingston drive. I know the drive is OK because I used it as an OS drive a few days ago. Its currently reformatted from within Win 7 Setup.
If the drive was the problem I dont see how that could be stopping my system from posting and getting into bios.
I have the kingston in one of the Sata II ports. In a few days I'm going to try to install a sata DVD burner. I'll see if maybe these ports are just bad.

If you move down from the boot override, there is another option called [Hard Drive BBS Properties]. Just go in there, and set your Crucial as your boot drive, and I think you may be able to have this trouble resolved.